1. Field of the Invention
This invention pertains to sorting machines that optically sort or separate acceptable homogeneous products from unacceptable homogeneous products and other, non-homogeneous articles as the products and articles flow past a viewing window of such a machine on the basis of color classifications and weights.
2. Description of the Prior Art
A typical sorting machine of the type with which the present invention is used is a high speed sorting machine typically used for sorting homogeneous products in the food industry or otherwise. For example, individual coffee beans are caused to flow by gravity feed down a steep channel or chute to be sorted by such a machine to separate "unacceptable" beans from "acceptable" ones. The term "unacceptable" applies to beans that are outside of a predetermined acceptable range of "color" hue in one or more wavelength bands of light, which bands are in some cases outside of the visible color spectrum. In the simplest case, the items are sorted for variation from a hue or shade of color, including a shade of black or white and thus a shade of gray, in a single spectrum. Such a sorting procedure is referred to as monochromatic sorting since only a single radiation spectrum is being observed. In a more complex optical color sorting operation, the flow of items is sorted to determine when an item is reflecting an unacceptable radiation amount in either of two wavelength bands. Such a sorting procedure is referred to as bichromatic sorting. It will be apparent that more than two radiation bands can be employed, if desired.
Optical sorting machines of the type generally described above employ optical sensors that include one or more photodetectors, such as photodiodes. The photodetectors are positioned to observe the illuminated product stream through a light admitting viewing window. The stream of product passes between an optical sensor and a background having a color or shade that matches the product stream in standard color or shade, so that only a variation in a product color or shade causes a detection event. The illumination is from one or more lamps directed at the product stream to cause standard reflectivity from acceptable products in the one or more wavelength bands being observed and to cause unacceptable reflectivity from unacceptable products and articles in those bands.
The machines also include an ejector mechanism located downstream from the sensor or sensors and actuated by an electrical signal originating from sensor detection. When a unacceptable product or article is detected, an electrical signal is produced and the ejector is actuated just as the unacceptable product or article and the mechanism are in alignment. Therefore, there is a very slight delay time from the time of sensing to the time of ejecting, which varies depending on the weight of the product. The typical ejector mechanism is usually an air ejector that has a variable "dwell time." The dwell time of an ejector is the length of time the ejector is fired, which varies depending on the weight of the product.
As mentioned above, the product stream flows in front of a background having a color or shade that is critical to the overall operation in that it must match the product under detection in the wavelength band or bands being observed by the sensors. U.S. Pat. No. 4,235,342 ("'342 patent"), commonly assigned to the assignee of the present invention, provides a description of a mechanism for correcting any color variation in the background due to common problems such as dust accumulation and/or background fading or clouding. The '342 patent is hereinafter incorporated by reference for all purposes.
As the '342 patent shows, the apparatus accurately utilizes a programmable classifier to classify the product in accordance with the percentage reflectivity of two predetermined color wavelengths. The programmable classifier includes an electrical signal generator adapted to generate first and second electrical signals respectively representative of the intensity of light energy reflected from the product being sorted at respective first and second color wavelengths and a programmable memory element having a matrix array of storage locations therein. Each point in the array is addressable by a combination of electrical signals corresponding to the reflected light intensities at the first and second color wavelengths from a product being sorted. At least one profile containing addresses corresponding to reflectivities of an acceptable product is used to program the memory with an electrical signal representation of the acceptability of a product having reflectivities defining the addressed location.
The system is ready to sort product as soon as the memory is programmed. When an individual unacceptable product passes in front of the viewing window, an ejector control arrangement exposes substantially the same portion of each unacceptable product to be ejected with the pressurized jet. The delay time from detection of the product in the viewing window to when the product is opposite the ejector is preset and based on the weight of the products being sorted. The time of the exposure of the ejecting force to the product, i.e., the dwell time, is also preset and based on the weight of the product. Once the delay and dwell times are pre-selected and set, they do not vary during a product sorting session.
Typically, dwell times are adjusted to be longer than necessary to assure ejection of unacceptable product, even though, shorter dwell times might seem desirable, because accidental ejection of acceptable product located near the unacceptable products may occur if the dwell time is to long. In the sorting industry, however, it is more important to eject some acceptable product than to miss unacceptable product.
The apparatus described in the '342 patent is very effective in removing unacceptable product from a stream of only homogeneous product, wherein some of the product are defective and, thus, unacceptable. However, in common practice, the stream of product includes not only homogeneous, but non-homogenous articles, such as white rocks, black rocks, and other foreign material, such as sticks or nubs (small, shriveled peanuts). In some instance, these non-homogeneous articles are identified as unacceptable as they pass in front of the viewing window, but are not removed from the product stream by the ejector because the non-homogeneous articles travel faster than homogeneous products, or are so heavy that the ejector force required to remove them would remove too much acceptable product if the system were set-up to accommodate removal of heavy non-homogeneous articles.
Likewise, there are occasion when light non-homogeneous articles tend to slide through the viewing element more slowly than the homogeneous products and thus, would not be positioned at such appropriate time in front of the ejector for removal of such article from the product stream.
It is therefore a feature of the present invention to provide a sorting machine capable of automatically removing unacceptable homogeneous product as well as unacceptable non-homogeneous articles from a product stream.
It is another feature of the present invention to provide an improved method and a sorting apparatus and for automatically removing both unacceptable light weight and unacceptable heavy weight articles from the product stream.